1. Field of the Invention
The present invention relates, in general, to a field emission display (hereinafter referred to as "FED") and, more particularly, to a FED which has a tip of emitting electrons formed by slant etch. Also, the present invention is concerned with methods for fabricating the same.
2. Description of the Prior Art
A FED typically includes an electron emitter, a controller, and a light emitter. In a FED, electrons are generated in the electron emitter and proceed into a target under control of the controller. The electrons bombard with a fluorescent layer, a target, and then light is emitted therefrom. A tip, an essential component responsible for emitting the electrons in a FED, should be capable of transferring the electrons generated in a conductive cathode and accordingly, may be made of any conductive material. Presently, those materials such as silicon or metals have widely been used for the tip. However, silicon is virtually impossible to employ on a glass substrate.
In order to better understand the background of the invention, a description for conventional technique will be given below with reference to some figures.
Referring to FIG. 1, there is shown a conventional FED. As shown in this figure, the FED is comprised of two substrates, a lower glass substrate 10 and an upper glass substrate 15, and a functional structure sandwiched therebetween, wherein a conductive cathode layer 11 atop the lower glass substrate 10 has a tip 12 on a central area of its surface and an insulating layer 13 capped with a gate electrode 14 on the other area and a transparent electrode 16 underneath the upper glass substrate 15 is provided with a fluorescent layer 17 (for emitting light) at a central area of the lower surface thereof. The tip 12 is aligned with the fluorescent layer 17 in such a way that they may stand opposed to each other at a distance under a vacuum condition.
With regard to functions of the components, as mentioned above, the tip 12 emits electrons and the fluorescent layer 17 emits light as a result of the bombardment of the electrons, while the direction of the electrons is under control of the gate electrode 14.
FIG. 2 illustrates fabrication processes for the conventional FED. These fabrication processes are described in connection with FIGS. 2A through 2F.
With reference to FIG. 2A, a cathode layer 11, an insulating layer 13 and a gate electrode layer are in sequence deposited entirely over a glass substrate 10 by a sputtering or CVD process, and a central part of the gate electrode layer is taken off by a combination of photomasking process and reactive ion etching (hereinafter referred to as "RIE") process, to form a gate electrode 14 responsible for controlling the emission of electron.
With reference to FIG. 2B, the insulating layer 13 is subjected to wet chemical etching or RIE, to expose a predetermined area of the conductive cathode layer 11, with the gate electrode 14 serving as a mask. At the moment, the insulating layer is over-etched in order to provide a space wherein, as will be described later, a sharp-pointed tip is formed.
With reference to FIG. 2C, a nickel layer is deposited entirely over the gate electrode 14 and patterned to form a mask layer 18 which is used for depositing a tip layer later, followed by deposition of a tip layer 19 on both the mask layer 18 and the exposed area of the conductive cathode layer 11. Upon evaporating the tip layer 19, a tip 12 is formed on the exposed area of the glass substrate 10 at an angle of 75 degrees to the surface of the glass substrate 10 since the glass substrate 10 is rotated.
With reference to FIG. 2D, an electrochemical etching process is executed so as to eliminate the mask layer of nickel 18 as well as the tip layer 19.
Separately from the processes illustrated in FIGS. 2A to 2D, a blank transparent electrode 16, as shown in FIG. 2E, is deposited over another glass substrate 15, followed by deposition of a fluorescent layer 17 of phosphor on the transparent electrode 16. The fluorescent layer 17 is patterned by photolithography, to prepare it for emitting light.
With reference to FIG. 2F, the tip 12 is aligned with the fluorescent layer 17 in such a manner that they may stand opposed to each other at a distance with vacuum maintained therebetween.
In such conventional FED, when an electric field of a considerable amount of negative voltage, for example, about -200 to about -1000 volts, is applied to the tip 12, electrons are emitted from the tip 12. Light is illuminated from the fluorescent layer 17 when the emitted electrons bombard the fluorescent layer 17 (which is applied with some positive voltages.)
If some positive volts are applied to the gate electrode 14, the electrons emitted from the tip 12 cannot reach the fluorescent layer 17 but are absorbed in the gate electrode 14 and thus, no light is emitted.
As stated above, whether the fluorescent layer 17 emits light or not is determined by varying the voltage applied to the gate electrode 14 under the condition that desirable values are set on the respective voltages applied to the tip 12, an electron emitter, and the fluorescent layer 17, a light emitter.
Establishment of vacuum state in the FED is intended to transfer electrons from the tip 12 to the fluorescent layer 17 only by electric field.
However, since the tip is formed on the conductive cathode (by evaporating the tip layer) on the glass substrate at an angle of 75 degrees to the surface of the glass substrate, the fabrication processes for the conventional FED are considerably difficulty to perform in addition to being complicated. So, the fraction of conventionally manufactured FEDs that are defective is very high. Further, the mask layer is only a temporary structure used while forming the tip. As a result, this nickel layer is sacrificial, i.e., not retained in the FED, which increases the production cost of the FED.